I. Field
The following description relates generally to wireless communications, and more particularly to facilitating pre-signaling supplemental wireless nodes to enhance wireless coverage in a network deployment.
II. Background
Wireless communication systems are widely deployed to provide various types of communication content, such as voice content, data content, and so on. Typical wireless communication systems can be multiple-access systems capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, . . . ). Examples of such multiple-access systems can include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, and the like. Additionally, the systems can conform to specifications such as third generation partnership project (3GPP), 3GPP long term evolution (LTE), ultra mobile broadband (UMB), or multi-carrier wireless specifications such as evolution data optimized (EV-DO), one or more revisions thereof, etc.
Generally, wireless multiple-access communication systems can simultaneously support communication for multiple mobile devices. Each mobile device can communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to base stations. Further, communications between mobile devices and base stations can be established via single-input single-output (SISO) systems, multiple-input single-output (MISO) systems, multiple-input multiple-output (MIMO) systems, and so forth.
A recent technological advancement in wireless communication is the integration of relatively small, low power base stations or wireless access points within existing macro base station deployments. These low power base stations can be governed by a nearby macro base station, or can be treated as independent base stations by a wireless network. Typically, low power base stations can be deployed indoors, such as within a shopping mall, office building, apartment complex, etc., to provide targeted cellular coverage to a given building, or dispersed outdoors within poor coverage areas, for instance, to provide targeted cellular coverage for a particular geographic region. These base stations have multiple advantages for supplementing a macro deployment. First, small low power base stations are generally less expensive than full macro base stations, and can supplement a macro deployment at lower cost. Second, because these base stations typically transmit at much lower power and over shorter ranges, a supplemental deployment of low power base stations can be tailored to limit interference to a surrounding network.
Various types of supplemental or low power base stations exist. One common example is a relay node. A relay node refers to a base station-like entity that may or may not be coupled to a wired backhaul. Further, the relay node is generally a low power base station with small coverage area in relation to a typical 50 watt or similar macro base station. In addition, the relay node is typically subservient to and controlled by one or more donor macro base stations.
In operation, a relay node receives data over-the-air from a donor base station, and can forward that data to an access terminal (AT) served by the relay node (and by the donor base station). The relay node can forward the data to the AT utilizing the same wireless spectrum as the donor base station (an in-band relay), or can receive the data on a first spectrum and retransmit that data on a second spectrum (an out-of-band relay). The in-band relay is often a half duplex entity, that can either transmit or receive in a given time frame, but not both, whereas the out-of-band relay can often be full duplex, capable of simultaneous reception and transmission (on different frequency bands).
In addition to the general characteristics described above, several variations of relay nodes exist. For instance, a transparent relay node refers to a relay node that is not visible to, or is not recognized as a separate entity by, the AT. Rather, the transparent relay is indistinguishable from the donor base station, at least from the perspective of the AT. Transparent relays, therefore, typically just repeat cell identity information, acquisition and synchronization information, and so on, of the donor base station. One common function of the transparent relay is to boost transmit power of the donor base station. In some cases, the transparent relay can decode, filter, and then retransmit those signals, to provide a higher quality signal, as opposed to just providing an increase in signal amplitude. One particular relay, called an incremental redundancy relay (an IR relay), can monitor base station scheduling messages over-the-air, and identify data or control traffic intended for the AT. The IR relay can demodulate downlink data sent by the base station and can assist in subsequent hybrid automatic repeat request (HARQ) transmissions of the downlink data to the AT (e.g., if the AT indicates that a portion or all of the data is not received). Similarly, the IR relay can decode uplink data transmissions from an AT and can assist in subsequent HARQ transmissions of the uplink data. Because the IR relay generally observes a better signal to noise ratio (SNR) for this traffic than the AT, it can decode the traffic earlier and reduce timing for subsequent HARQ transmission (as compared with HARQ transmissions of a more distant base station).
Although relay nodes have several advantages, some drawbacks and design challenges do exist concerning integrating these entities into a macro deployment. For instance, half duplex nodes have fewer transmit and receive resources, due to the nature of half duplex operation. This tends to reduce efficacy of the relay node and can lower potential loading capabilities (e.g., how many ATs can be served concurrently). In addition, complexities arise in managing control signaling between the base station and relay node, or between the base station and ATs, since ATs are generally configured to look for certain control signals in particular time slots, some of which may not be available as transmission slots to a half duplex relay node. These and other challenges are the focus of current research in wireless networking.